Stereoscopic user interface method and apparatus

ABSTRACT

A computer system stereoscopically projects a three dimensional object having an interface image in a space observable by a user. The user controls the movement of a physical object within the space while observing both the three dimensionally projected object and the physical object. The computer system monitors the position of the user to determine the position of the interface image within the space and further monitors the movement of the physical object to determine its position. A control signal is generated in response to the position of the physical object intersecting the position of the interface image. For example, a word processing program is indicated by an interface image such as an icon including the letter &#34;W&#34; three dimensionally projected within the space. The word processing program is activated when the user&#39;s finger moves within the space to touch the projected icon. The interface allows the user to observe the projected icon, physical finger and their intersection within the space. The physical object may also be extended with a stereoscopic extension image generated by the computer system in response to determining the position and orientation of the physical object.

FIELD OF THE INVENTION

This invention generally relates to the area of computer user interfacesand more particularly to virtual three dimensional user interfaces.

BACKGROUND OF THE INVENTION

Graphical user interfaces have become a standard for interfacing betweena user and a computer. Such interfaces are in wide use in computeroperating system interfaces produced by Apple, Microsoft and others.These interfaces are limited in that they are intended for interfacingbetween a user and a computer having a two dimensional display such as aCRT or LCD. A user activates the interface with a key board and or apointing device such as a mouse pointing to an icon on the display.Advancements have been made with the advent of a touch screen whichallows a user to approximately contact the icon or intended area of thegraphical user interface in order to use the interface. However, contactwith the touch screen can contaminate the display area of the screenwith finger prints and other types of smudges. Also, constant physicalcontact with the touch screen can result in its mechanical failure.Thus, what is needed is a way to contact user interface images withoutcontacting a keyboard or a mouse or the display itself.

Three dimensional image displays are improving. Several types of threedimensional displays are known including stereoscopic displays whichdisplay a virtual three dimensional image using filters to highlightimages intended for each eye of the viewer, thereby providing astereoscopic or three dimensional affect. Such systems alternately flashimages for the left and right eye of the user and require a filter foreach eye, usually included in glasses worn by the viewer. Systems are inpublic use which require glasses may have color filters, orthogonallypolarized lenses, or actively switched lenses, and the display iscorrespondingly modulated with left and right eye images to provide thethree dimensional effect. Furthermore, stereoscopic displays which donot require glasses have been described, descriptions are included inU.S. Pat. No. 4,987,487, Jan. 22, 1991, to Ichinose et al. entitledMethod of stereoscopic images display which compensates electronicallyfor viewer head movement, and U.S. Pat. No. 5,365,370, Nov. 15, 1994, toHudgins entitled Three dimensional viewing illusion with 2D display. Yetanother stereoscopic display system in completely contained in a headset worn apparatus as described in U.S. Pat. No. 5,673,151 Sep. 30, 1997to Dennis entitled Image correction in a virtual reality and heads updisplay. The aforesaid patents are incorporated by reference. Theaforesaid stereoscopic displays allow the viewer to simultaneouslyobserve both a stereoscopic object, appearing to be generally set apartin three dimensions from the image projection means, and a physicalobject, such as the hand of the user, in approximately the sameperceived space. What is needed is a method and apparatus by which theintersection of the physical object and the stereoscopic object can forma user interface with a computer system.

OBJECT OF THE INVENTION

It is therefor an object of the invention to provide a three dimensionaldisplay system capable of determining an intersection of a physicalobject with a three dimensionally displayed object in a space where thethree dimensional object is viewed and generating a control signal inresponse thereto. The control signal may cause modification of thedisplayed image or control another device. The display system is alsocapable of extending the physical object with a three dimensionalextension image and then using the extended image to determine theintersection.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of a user causing an intersection of aphysical object with a three dimensional stereoscopic object projectedby a display.

FIG. 2 shows the display of the stereoscopic interface image.

FIG. 3 shows determination of the position of the stereoscopic interfaceimage.

FIG. 4 shows a physical object intersecting the stereoscopic interfaceimage.

FIG. 5 shows a stereoscopic extension of the physical objectintersecting the stereoscopic interface image.

FIG. 6 shows a stereoscopic extension image of the physical objectintersecting the stereoscopic interface image wherein the intersectionis behind the display.

FIG. 7 shows a block diagram of the user interface system operating inaccordance with the present invention.

FIG. 8 shows a flow chart of a process operating in accordance with thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a perspective view of a user causing an intersection of aphysical object with a three dimensional stereoscopic object projectedby a display. The user 100 has left and right eyes 110 and 120 which areused to view a display 200 which projects a three dimensionalstereoscopic object 245 in a space between the user and the display. Thestereoscopic object has a stereoscopic interface image 250. Usingpattern recognition and triangulation, images from video cameras 310 and320 are used to determine the position of physical objects within thespace, such as the position of the user 100 and the user's finger 400.As will be described herein, a control signal is generated in responseto the intersection of the interface image 250 and a physical object400. For example, the stereoscopic object 245 projected by the display200 could be the image of an open book, including readable text on pagesof the book. Interface image 250 could be an icon indicating thatcontact with the icon would cause a page in the book to turn. When thefinger tip 400 of the user touches the icon 250, a control signal isgenerated causing a new image 245 of a book to be displayed with aturned page. The stereoscopic three dimensional image has the advantageof being projected in a space, no physical contact with a keyboard,mouse or touch screen is needed to generate a control signal to turn apage of the book. Rather, an intuitive action of a user appearing tomake physical contact with a three dimensional image in the space causesgeneration of the control signal. The user sees the interface image in athree dimensional space and simply uses a finger to touch the interfaceimage to cause a response. The user has an actual view of the finger,with which the user has had a life time to become familiar. touching avirtual stereoscopic object similar to the way the user has spent a lifetime touching physical objects. This provides for an intuitiveinterface.

The stereoscopic projector 200 can be any of several display meanscapable of displaying three dimensional images. Some projectors requirethe user to wear colored, polarized of active image filter glasses (notshown) to observe the three dimensional image while others are totallycontained within a display headset worn by the user, yet anotherrequires only a display separate from the user and no glasses at all.While all displays capable of displaying a three dimensional image arecontemplated, the latter is preferred because of the convenience to auser requiring no physical contact with the means necessary to displaythree dimensional images.

FIG. 2 shows the display of the stereoscopic interface image. Display200 displays an image 210 for viewing by the left eye 110 of the user100 while image 220 displayed for viewing by the right eye 120 of user100. As a result, stereoscopic interface image 250 appears to occur in aspace between the user 100 and the display 200 at a position indicatedby the intersection of a line from eye 110 to image 210 and a secondline from eye 120 to image 220.

FIG. 3 shows determination of the position of the stereoscopic interfaceimage. The position is dependent upon the distance between images 210and 220, the distance between the eyes 110 and 120 of the user 100 andthe position of the user including distance D1 between the display 200and the user. Preferably, the size of display 200 is predetermined andthe image 250 is determined by the computer generating the image.Consequently the distance between images 210 and 220 is alsopredetermined. The distance between the eyes 110 and 120 can be enteredby the user as a calibration procedure prior to operating the userinterface means, or can be determined by pattern recognition from imagesrecorded by cameras 310 and 320. The position of the user including thedistance between the user and the display can determined by patternrecognition by the images recorded by cameras 310 and 320 to determine acommon point relative to the user. Pattern recognition of images offaces and other physical objects are well known, such descriptions canbe found in references including U.S. Pat. No. 5,680,481 Oct. 21, 1997to Prasad et al. entitled Facial feature extraction method and apparatusfor a neural network acoustic and visual speech recognition system, U.S.Pat. No. 5,715,325 Feb. 3, 1998 to Bang et al. entitled Apparatus andmethod for detecting a face in a video image, and U.S. Pat. No.5,719,951 Feb. 17, 1998 to Shackeleton et al. entitled Normalized imagefeature processing, which are hereby incorporated by reference. Thecommon point may be the area between the eyes of the user. Alternately,the identification of the common point may be simplified by adding afiducial mark at the desired point to assist in identifying the desiredpoint and its corresponding angle. Such a mark could be a colored dotplaced between the eyes or at the tip of the nose, or marks on glassesworn by the user, the mark could be further illuminated to simplifypatter recognition of images received by the video camera. Thereafter,triangulation is performed to determine the position of the userincluding D1. D1 is a geometric solution of a predetermined distancebetween cameras 310 and 320 angles A1 and A2 found from images recordedby cameras 310 and 320. Thus, the position including D2 of interfaceimage 250 is readily geometrically determined from the aforesaiddeterminations. It should be appreciated that the three dimensionaldisplay means can be constructed such that the position of the user andthe distance D1 is predetermined in order for the user to correctly viewthe stereoscopic effect. Furthermore, the distance between the eyes 110and 120 can also be predetermined to be an average distance between eyesof a number of users. This simplifies determination of the position ofinterface image 250 without departing from the spirit and scope of theinvention. FIG. 3 shows determining the position of interface image 250from a top view, it should be appreciated that a similar analysisapplies to determining the position of interface image 250 from a sideview, thus providing a three dimensional position of the user 100 andthe interface image 250.

FIG. 4 shows a physical object intersecting the stereoscopic interfaceimage. Physical object 400 can be any physical object where the positionof the object can be determined. In FIG. 1, the physical objectcorresponds to the tip of the finger of the user. Pattern recognition isused to determine the position of the physical object and the tip of thefinger of the user. Alternately a fiducial mark such as theaforementioned colored or illuminated dot may be added to assist patternrecognition. Once the desired point is identified from the imagesrecorded by cameras 310 and 320, angles A3 and A4 may be determined.Given angles A3 and A4, and the predetermined distance between cameras310 and 320, the position of the physical object 400 may begeometrically determined. FIG. 4 shows determining the position of thephysical object from a top view, it should be appreciated that a similaranalysis applies to determining the position of the physical object froma side view, thus providing a three dimensional position of physicalobject 400. Upon determination of a substantial intersection of theposition of interface image 250 and physical object 400, a controlsignal is generated. The control signal may result in the modificationsof the image or the control another device such as a printer or modem.

FIG. 4 shows a computer system which stereoscopically projects a threedimensional object having an interface image in a space observable by auser. The user controls the movement of a physical object within thespace while observing both the three dimensionally projected object andthe physical object. The computer system monitors the position of theuser to determine the position of the interface image within the spaceand further monitors the movement of the physical object to determineits position. A control signal is generated in response to the positionof the physical object intersecting the position of the interface image.For example, a word processing program is indicated by an interfaceimage such as an icon including the letter "W" three dimensionallyprojected within the space. The word processing program is activatedwhen the user's finger moves within the space to touch the projectedicon. The interface allows the user to observe the projected icon,physical finger and their intersection within the space.

FIG. 5 shows a stereoscopic extension of the physical objectintersecting the stereoscopic interface image. In this alternativeembodiment, the physical object is shown as a bar 450 having a first andsecond end 452 and 454 with a stereoscopic extension image 255projecting from end 454. The orientation and position of the physicalobject is determined by determining the positions of end points 452 and454 from images recorded by cameras 310 and 320. The end points can befound by pattern recognition or by adding of differing colored fiducialmarks at either end of the bar. The position of end point 452 may bedetermined from angles A6 and A8 of images from cameras 310 and 320respectively while the position of end point 454 may be determined fromangles A5 and A7 from cameras 310 and 320 respectively. FIG. 5 showsdetermining the position of the end points from a top view, it should beappreciated that a similar analysis applies to determining the positionof the end points from a side view, thus providing a three dimensionalposition of end points 452 and 454. From the position of the two endpoints, the orientation of the physical object 450 may be determined. Inresponse to the determined position and orientation of physical object450 and the determined position of user 100, a stereoscopic extensionimage 255 is created such that the extension image appears to be anextension of the physical object. In FIG. 5, the extension image 255 isshown as a line extending along the line of physical object 450 with anarrow head tip. The length and shape of the extension image ispredetermined and may vary from application to application. Thestereoscopic extension image 255 is created by displaying images 215 and225 on display 200 for view by eyes 110 and 120 respectively. A controlsignal is generated when the position of a predetermined portion of thestereoscopic extension image, such as the tip of the arrow head,intersects the position of the stereoscopic interface image.

FIG. 6 shows a stereoscopic extension image of the physical objectintersecting the stereoscopic interface image wherein the intersectionis behind the display 200. FIG. 6 is similar to FIG. 5 in that both showa stereoscopic extension image, 255 and 255', intersecting astereoscopic interface image, 250 and 250'. However in FIG. 5 theintersection is in front of display 200, while in FIG. 6 theintersection is behind display 200. The position and orientation ofphysical object 450 is determined by determining the position of endpoints 452 and 454 via cameras 310 and 320 and angles A5', A6', A7' andA8'. In this case the resulting extension image 255' is shown to have asubstantially longer predetermined length than image 255 of FIG. 5. Ifdisplay 200 were not a heads-up stereoscopic display, but rather aconventional LCD or CRT, then the intersection between a physical objectand an interface image could not occur if the position of the interfaceimage were behind the display because either the space is physicallyoccupied by another object or the user could not see the physicalintersection through the display. The extension image has the advantageof enabling intersections to occur in positions appearing behind thedisplay 200, or in other positions out of reach of the user, whileallowing the user to directly view the physical object used to cause theintersection.

Physical object 450 has been referred to as a bar, but it should beappreciated that the physical object could be any of a number ofphysical objects including the finger of the user where one end is thefinger tip and the other end is a joint of the finger. Fiducial markscould be added to the points on the finger to facilitate patternrecognition of images recorded by the cameras. While the extension imageis shown as a line with an arrow head, other types of extension imagesmay be used depending upon the application. The stereoscopic extensionmay be considered a virtual end effect for a physical handle, a widevariety of end effects may be created by the computer system. Forexample a paint brush could be used for paining a virtual object, thehandle being the physical object and the brush bristles and paint colorthe being end effect while the interface image appears as a paint canvasmounted on and three dimensional easel image. In a medical application,the physical object could be the handle and the end effect extensionimage the blade of a scalpel while the stereoscopic interface image partof a three dimensional image simulating surgery. Alternately in a gameapplication the stereoscopic extension image could be a laser beam,rocket, bullet or bolt of lightning appearing to emanate from the fingerof the user along a three dimensional vector defined by the finger, thestereoscopic interface image may be a villain or enemy tank moving inthree dimensions.

It should also be appreciated that the position and orientation of theuser 100 and physical object 450 have been described as being determinedby two cameras with pattern recognition which triangulate in order todetermine the corresponding position and orientation. In a heads upstereoscopic head set display, the cameras could be preferably mountedon the head set for visually monitoring physical objects in same spacein which the user observes the projected stereoscopic images. Inalternate embodiments other techniques may be used to determine theaforesaid positions and orientations without departing from the spiritand scope of the invention.

FIG. 7 shows a block diagram of the user interface system operating inaccordance with the present invention. A stereoscopic display 200displays stereoscopic images generated by stereoscopic image generationmeans 212 in a manner know in the art. The stereoscopic display may be aCRT or LCD screen requiring filter glasses to be worn by the user todirect the appropriate image to the corresponding eye of the user.Alternately, it may be a heads up stereoscopic display worn by the user.Preferably display 200 is a display means especially adapted todisplaying stereoscopic images without the aid of devices worn by theuse. Cameras 310 and 320 produce images which are analyzed by patternrecognizers 312 and 322 which identify certain points of the image andtheir location within the image. As previously described, the patternrecognition may be performed with or without the aid of fiducial marks.The location of the points from pattern recognizers 312 and 322 areanalyzed by coordinate determining means 314 which analyzes the anglesrelative to each point from each camera, and knowing the predetermineddistance between the cameras, is able to determine the desired positionsand orientations. Coordinate determining means 314 also makes availablethe position of the user and the position and orientation of thephysical object so that the stereoscopic image generator 212 maygenerate the stereoscopic extension image in response thereto.Coordinate determining means 314 also makes available the position ofthe user to coordinate determining means 214 which determines theposition of the interface image relative to the user by determining thedistance between the left eye and right eye images displayed on display200 with the user's position including the distance between the user andthe display and the spacing between the eyes of the user. The positionsof the physical object and interface image are then compared byintersection monitor 322 which generates a control signal in response toa substantial coincidence with the position of the physical object, orits stereoscopic extension image, and the position of the stereoscopicinterface image.

FIG. 8 shows a flow chart of a process operating in accordance with thepresent invention. In step 800, a stereoscopic image is displayed. Step802 determines the position of the user as previously described. Note inalternate embodiments the position of the user may be predetermined.Then in step 804 the position of the stereoscopic interface imagerelative to the user is determined. Step 806 determines the position andorientation of the physical object and step 810 asks if and extensionimage is desired. If so, step 812 causes the display of the extensionimage and step 814 redetermines the position and orientation of thephysical object with the extension image. Then step 816 determines ifthere is an intersection between the interface image and the physicalobject or its extension image. If so, step 818 generates a controlsignal which in step 820 modifies the displayed image and/or controlsanother device.

Thus what has been provided is a method and apparatus by which theintersection of a physical object and a stereoscopic object can bedetermined and be used to form a user interface with a computer system.

I claim:
 1. A method of displaying a stereoscopic extension image as anextension of a physical object observable by a user comprising the stepsof:determining a position and orientation of the physical object; anddisplaying the stereoscopic extension image also observable by the useras the extension of the physical object in response thereto, whereinsaid step of displaying further comprises the step of determining aposition of the user, and includes projecting the stereoscopic extensionimage relative to the determined position of the user and said step ofdetermining the orientation of the physical object further comprises thesteps of:visually recognizing a first and a second point on the physicalobject; determining a position of the first point and the position ofthe second point; and determining coordinates of a line defined by thepositions of first and second points; and further wherein said step ofdisplaying projects the stereoscopic extension image substantially alongthe line as observed by the user.
 2. The method according to claim 1wherein the physical object is a handle having at least the first andsecond points and the stereoscopic extension image is a projection of anend effect on the handle.
 3. The method according to claim 1 wherein thestereoscopic extension image is a projection of one of a plurality ofselectable end effects.
 4. The method according to claim 1 furthercomprising the steps of:displaying a stereoscopic interface imageobservable by the user; determining an intersection of the stereoscopicextension image with the stereoscopic interface image; and generatingthe control signal in response thereto.
 5. A method of generating acontrol signal comprising:projecting a stereoscopic interface image in aspace observable by a user; enabling a physical object within in thespace to be observable by the user in addition to the stereoscopicinterface image; determining an intersection of the physical object withthe stereoscopic interface image; and generating the control signal inresponse to said step of determining wherein the physical objectincludes a stereoscopic extension image and the method further comprisesthe steps of:determining a position and orientation of the physicalobject; and displaying the stereoscopic extension image as an extensionof the physical object in response thereto, whereinsaid step ofdetermining the intersection further comprises the step of determiningan intersection of the stereoscopic extension image with thestereoscopic interface image and further whereinsaid step of projectingthe stereoscopic interface image is projected by a display having adisplay surface and the space includes a front space between the displaysurface and the user and a behind space behind the display surface andwherein the stereoscopic interface image is projected in either thefront space or the behind space, said step of displaying thestereoscopic extension image displays the stereoscopic extension imagein either the front space or the behind space, and said step ofdetermining the intersection further comprises the step of determiningthe intersection of the stereoscopic extension image with thestereoscopic interface image in either the front space or the behindspace.
 6. The method according to claim 5 whereinsaid step of projectingfurther projects an observable image including the stereoscopicinterface image and the method comprises the step of modifying theobservable image in response to the control signal.
 7. The methodaccording to claim 6 further comprising the step ofdetermining aposition of the user, wherein said step of determining the intersectiondetermines the intersection of the physical object and the stereoscopicinterface image relative to the position of the user.
 8. The methodaccording to claim 7 further comprising the step ofvisually monitoringthe user and the physical object, and wherein said step of determiningthe position of the user is determined in response to said step ofvisually monitoring, and said step of determining the intersection ofthe physical object with the stereoscopic interface image is determinedin response to said step of visually monitoring.
 9. The method accordingto claim 5 further comprising the step ofvisually monitoring thephysical object, and wherein said step of determining the intersectionof the physical object with the stereoscopic interface image isdetermined in response to said step of visually monitoring.
 10. A methodof generating a control signal comprising:projecting a stereoscopicinterface image in a space observable by a user; enabling a physicalobject within in the space to be observable by the user in addition tothe stereoscopic interface image; determining an intersection of thephysical object with the stereoscopic interface image; and generatingthe control signal in response to said step of determining wherein thephysical object includes a stereoscopic extension image and the methodfurther comprises the steps of:determining a position and orientation ofthe physical object; and displaying the stereoscopic extension image asan extension of the physical object in response thereto, whereinsaidstep of determining the intersection further comprises the step ofdetermining an intersection of the stereoscopic extension image with thestereoscopic interface image and further whereinsaid step of projectingthe stereoscopic interface image is performed by a display having adisplay surface viewable by the user and the space includes a behindspace behind the display surface and wherein the stereoscopic interfaceimage is projected in the behind space, said step of determining theposition and orientation of the physical object includes determining aposition and orientation of the physical object to be between the userand the display surface, said step of displaying the stereoscopicextension image displays the stereoscopic interface image in the behindspace, and said step of determining the intersection further comprisesthe step of determining an intersection of the stereoscopic extensionimage with the stereoscopic interface image in the behind space.
 11. Themethod according claim 10 wherein the display surface substantiallyinhibits the user's observation of physical objects in the behind space.12. The method according to claim 10 whereinsaid step of projectingfurther projects an observable image including the stereoscopicinterface image and the method comprises the step of modifying theobservable image in response to the control signal.
 13. The methodaccording to claim 10 further comprising the step ofdetermining aposition of the user, wherein said step of determining the intersectiondetermines the intersection of the physical object and the stereoscopicinterface image relative to the position of the user.
 14. The methodaccording to claim 13 further comprising the step ofvisually monitoringthe user and the physical object, and wherein said step of determiningthe position of the user is determined in response to said step ofvisually monitoring, and said step of determining the intersection ofthe physical object with the stereoscopic interface image is determinedin response to said step of visually monitoring.
 15. The methodaccording to claim 10 further comprising the step ofvisually monitoringthe physical object, and wherein said step of determining theintersection of the physical object with the stereoscopic interfaceimage is determined in response to said step of visually monitoring. 16.A stereoscopic user interface means for generating a control signalcomprising:a display means for projecting a stereoscopic interface imagein a space observable by a user wherein said display means enables aphysical object within in the space to be observable by the user inaddition to the stereoscopic interface image; and a monitoring means fordetermining an intersection of the physical object with the stereoscopicinterface image and for generating the control signal in responsethereto, wherein the physical object includes a stereoscopic extensionimage and the stereoscopic user interface means further comprisesacoordinate determining means for determining a position and orientationof the physical object, and whereinsaid display means displays thestereoscopic extension image as an extension of the physical object inresponse to said coordinate determining means, and said monitoring meansdetermines an intersection of the stereoscopic extension image with thestereoscopic interface image to generate the control signal and furtherwhereinsaid display means has a display surface and the space includes afront space between the display surface and the user and a behind spacebehind the display surface and wherein the stereoscopic interface imageis projected in either the front space or the behind space, thestereoscopic interface image is displayed in either the front space orthe behind space, and said monitoring means determines intersection ofthe stereoscopic extension image with the stereoscopic interface imagein either the front space or the behind space.
 17. The stereoscopic userinterface means according to claim 16 further comprisinga coordinatedetermining means for determining a position of the user, wherein saidmonitoring means determines the intersection of the physical object andthe stereoscopic interface image relative to the position of the user.18. A stereoscopic user interface means for generating a control signalcomprising:a display means for projecting a stereoscopic interface imagein a space observable by a user wherein said display means enables aphysical object within in the space to be observable by the user inaddition to the stereoscopic interface image; and a monitoring means fordetermining an intersection of the physical object with the stereoscopicinterface image and for generating the control signal in responsethereto, wherein the physical object includes a stereoscopic extensionimage and the stereoscopic user interface means further comprisesacoordinate determining means for determining a position and orientationof the physical object, and whereinsaid display means displays thestereoscopic extension image as an extension of the physical object inresponse to said coordinate determining means, and said monitoring meansdetermines an intersection of the stereoscopic extension image with thestereoscopic interface image to generate the control signal and furtherwhereinsaid display means has a display surface viewable by the user andthe space includes a behind space behind the display surface and whereinthe stereoscopic interface image and the stereoscopic extension imageare projected in the behind space, said coordinate determining meansdetermining the position and orientation of the physical object to bebetween the user and the display surface, and said monitoring meansdetermines the intersection of the stereoscopic extension image with thestereoscopic interface image in the behind space.
 19. The stereoscopicuser interface means according to claim 18 whereinsaid display meansfurther projects an observable image including the stereoscopicinterface image, and the stereoscopic user interface means comprisesanimage generation means for modifying the observable image in response tothe control signal.
 20. The stereoscopic user interface means accordingto claim 18 further comprisinga coordinate determining means fordetermining a position of the user, whereinsaid monitoring meansdetermines the intersection of the physical object and the stereoscopicinterface image relative to the position of the user.